Cleaning and preserving of metallic surfaces



252. COMPOSITIONS,

Patented June 2, 1931 UNITED STATES Ham PATENT OFFICE DEAL H. TOMPKINS, 0F NITRO, WEST VIRGINIA, ASSIGNOR TO THE RUBBER SERVICE LABORATORIES COMPANY, OF AKRON, OHIO, A CORPORATION OF OHIO CLEANING AND FBI-SERVING OF METALLIC SURFACES No Drawing.

The present invention relates to the cleaning and preservation of metallic surfaces, wherein the metal is in contact with a liquid of an acid nature. More particularly, the invention relates to the prevention of excessive pitting and embrittlement of a metal when subjected to a pickling process by treatment with a dilute solution of a non-oxidizing acid.

Certain objects accomplished by means of the present invention are to prevent the acid pickle liquor from attacking clean portions of the surface of a metal; to obviate overpickling, embrittlement and pitting of the articles treated; to minimize the amount of meal lost in pickling; to increase the efficiency of the pickling operation and to prolong the efl'ective life of the pickling bath and particularly to speed the pickling operation. Other and further objects of the invention will be apparent from the following description and accompanying examples.

In the art of pickling, the metal is treated with a dilute acid to remove oxides such as rust, scale, and other deposits, after which the metal is preferably washed with water and dipped into an alkaline bath to remove the last traces of free acid. The acid removes the rust and scale, but unfortunately, from the pickling standpoint, it attacks the clean metal itself thereby causing loss of metal and producing an evolution of hydrogen gas, which escapes into the air, carrying with it a fine spray of the acid liquor from the pickling bath and producing an atmosphere possessing corrosive properties and one which is injurious to health and damaging to equipment.

By the present invention, these objectionable features of the pickling process are substantially overcome or reduced to a minimum. To accomplish the objects set forth in accordance with thepresent invention, there is added to the pickling bath a regulating agent or ingredient which acts to restrain the action of the acid from attacking clean metal but assists in removing the rust, scale and other deposits, or in other Words the inhibitor causes the acid selectively to remove such materials without appreciably attacking the Application filed October 9, 1930. Serial No. 487,506.

clean portions of the metal under treatment.

The pickle regulator or inhibitor, as disclosed in the present application, comprises a hydrochloric acid derivative of a reaction product ofsulfur dioxide and an aldehydeamine reaction product and preferably a hydrochloric acid derivative of a reaction prodnot of sulfur dioxide and an aldehyde derivative of a Schifl"s base; that is, a product formed by reacting an aldehyde with a Schiffs base, adding sulfur dioxide thereto and treating the produQflso formed with hydrochloric acid of any concentration neces-- sary to produce chemical combination at the reaction temperature employed.

In the examples hereinafter set forth for carrying out the metal pickling process, conditions were imposed which duplicated, as far as possible, those commonly followed in commercial practice, so far as concerned acid concentrations and temperatures employed.

Test pieces of 30 gauge low carbon hot rolled steel sheets, approximately 4" x 3" in dimension were immersed in approximately 640 cc. of a water solution of sulfuric acid containing approximately 6% by weight of 66 B. acid to which had been added a small quantity of one of the preferred type of inhibitors. The loss in weight of the steel test pieces resulting from maintaining the strips in the pickle bath in the manner described for a definite period of time was then determined. The temperature of the pickling bath was maintained at from 17 6 to 185 F. (80 to 85 C.) For the acid concentration set forth, commercial practice is to pickle at approximately 150 to 190 F. (66 to 88 C.) The results so obtained were compared with similar tests wherein the steel pieces were subjected, under the conditions set forth, to the action of an acid solution of the strength and for the time specified above, but containing no inhibitor.

One method whereby one of the preferred class of compounds, for example a hydrochloric acid derivative of a reaction product of sulfur dioxide and an aldehyde derivative of a Schiffs base, was prepared as follows:

Substantially one molecular proportion of the product formed from the reaction of substantially three molecular proportions of acetaldehyde and substantially two molecular proportions of aniline, according to the method set forth in U. S. Patent No. 1,659,152 granted to Clayton Olin North, was dissolved in an organic solvent, for example, a quantity of acetone equal to one-third of the weight of the aldehyde-amine product. Substantially one-half a molecular proportion of sulfur dioxide was passed thereinto at a rate slow enough for complete absorption and combination to take place while agitating and maintaining a temperature of approximately 30 to 60 C. To the product thus formed, substantially one molecular proportion of hydrochloric acid, preferably having an acid strength of approximately 35 to 39% was added at a temperature of substantially 50 to 70 C. After the addition of the hydrochloric acid was completed, the water present and the solvent employed, for example acetone, were removed preferably by evaporation. The product prepared in the manner described, after cooling, was abrittle resin, which formed a fine powder when ground that was readily soluble in a pickle liquor as for example dilute sulfuric acid.

A sam le of the product prepared as described a ove was incorporated in a pickling bath in the manner hereinbefore described.

Thus, a steel test piece 3" x4" in dimension cut from 30 gauge low carbon hot rolled sheets, exposing approximately 24 square inches of surface and weighing 18.032 grams, was found to lose but 0.276 grams after minutes pickling in a 6% sulfuric acid solution containing 0.06 grams of the inhibiting product hereinbefore described. A similar test piece weighing 17.928 grams and treated in the same manner, but without the use of any inhibitor lost 7.165 grams. Thus it is shown when the hydrochloric acid derivative of the reaction product of sulfur dioxide and the product formed by reacting substantially three molecular proportions of acetaldehyde and substantially two molecular proportions of aniline is employed as an inhibitor, the loss in weight per square inch of surface exposed corresponds to 0.0115 grams, whereas when no inhibitor is employed in the test described, the loss per square inch of surface exposed corresponds to 0.2985 grams. The loss in weight per square inch of surface exposed is only 3.8% as great by employing the inhibitor set forth as results if no inhibitor is employed in the pickling process. A greater saving in metal losses results from the use of a larger amount of the inhibitor. Moreover, the steel plates ickled in the presence of the inhibitor set orth are clean and not stained upon removal from the bath.

Other hydrochloric acid derivatives of a reaction product of sulfur dioxide and an aldehyde-amine and preferably hydrochloric acid derivatives of a reaction product of sulfur dioxide and an aldehyde derivative of Schiifs bases have been prepared in a manner analogous to that hereinbefore set forth and tested as inhibitors in a pickling bath in the manner hereinbefore described.

Thus, a hydrochloric acid derivative of a sulfur dioxide reaction product of a Schiifs base and of aldehyde derivatives thereof as set forth hereinafter were prepared and the final product so obtained employed in a pickling bath and tested in the manner described. The products referred to in the results set forth in Table I, as Inhibitors A to G inclusive, represent the hydrochloric acid derivatives of the sulfur dioxide reaction product of the following bases:

Compound A.Anhydro fqgmaldehyde aniline.

Compound B.Reaction product of substantially three molecular proportions of ald e and substantially one molecular proportion of anilin e.

Compound C.Reaction product of substantially three molecular proportions of a cgtaldehyde and substantially two molecular proportions of ortho-tolujdine.

Compound D.-Rictioii product of substantially one molecular proportion of betaand substantially one nidle'cular proportion of formaldehyde.

Compound E'.Reaction product of substantially one molecular proportion of 9; tho-toluidine and substantially three molecular proportions of butylaldehyde.

Compound F.Reacti6h product of substantially one molecular proportion 0152 4- .slianiide. haalaaaa substantially three molecu ar'prop'ortions of heptaldehyde.

Compound C.-Reaction product of substantially one molecular proportion of anj: linerand substantially three molecular proportions of heptal dehyde.

The results of tests obtained on immersing steel test strips of 30 gauge low carbon hot rolled sheets 3" x 4 in dimension for forty minutes in 640 cc. of 6% by weight of 66 B. sulfuric acid at 80 C. containing one of the preferred inhibitors given above, are given in Table I.

. Table I Weight Weight of Weight of zf Inhibiting comof inhibsteel strip steel strip i pound employed itor embefore after 3 1222 ployed pickling pickling exposed Grams Grams Grams Grams Compound A 0. 06 18. 443 17. 946 0. 0207 Compound B 0. 06 18. 268 17. 900 0. 0153 Compound 0 0. 06 17. 571 17. 323 0. 0103 Compound D 0. 06 18. 823 18. 719 0. 0043 Compound E 0. 06 18. 611 18. 262 0. 0145 Compound F 0. 06 18. 497 18. 414 O. 0035 Compound G 0. 06 17. 063 17. 860 0.0043 None None. 17. 028 10. 763 0. 2985 It is thus apparent from the data set forth that the preferred class of materials 252. COMPOSITIONS,

constitutes an important and highly eificacious group of inhibitors, as in all cases wherein one of the preferred inhibiting compounds was incorporated in the pickle liquor, there resulted a great saving in the loss in weight of the steel test strips that resulted when no inhibitor was employed.

It has further been found that other ratios of hydrochloric acid, sulfur dioxide and aldehyde-amine than those hereinbefore set forth may be reacted and the reac ion product thus obtained employed as inhibitors. Thus, substantially one molecular proportion of the aldehyde derivative of a Schifls base formed by reacting substantially three molecular proportions of acetaldehyde with substantially two molecular proportions of aniline has been reacted with substantially seven-tenths of a molecular proportion of sulfur dioxide, and the material so prepared further reacted with substantially two molecular proportions of hydrochloric acid. The compound thus produced was incorporated in a pickle liquor in the manner hereinbefore described, the amount of inhibitor employed and the size and grade of steel sheets used being the same as in the above described tests. A sheet weighing 18.295 grams was found after pickling forty minutes to have lost but 0.304 grams, or 0.0127 grams per square inch of surface exposed. A sheet of the same stock weighing 17.928 grams and treated in the same manner, but with no inhibitor present, suffered a loss of 7.165 grams or 0.2985 grams per square inch of surface exposed.

Although it is desirable that the preferred inhibitor be prepared in the presence of an organic solvent, as for example acetone, benzene and the like, it is not imperative that a solvent be employed. Thus, sulfur dioxide may be reacted with the aldehyde-amine product without dissolving the latter in a solvent, and the product so formed may be further reacted with hydrochloric acid to form a compound of the preferred class and possessing the inhibiting qualities disclosed.

Other modes of employing inhibitors of the class hereinbefore set forth in the acid pickling of metals are apparent to those skilled in the art to which this invention pertains. The products described additionally may be employed in the presence of foaming agents, ionizable substances or other materials ordinarily used and are employable with the various acids commonly employed commercially in the acid pickling of metals.

What is claimed is:

1. A process of pickling a metal which comprises subjecting the metal to be pickled to the action of a substantially non-oxidizing mineral acid solution containing a small proportion of a hydrochloric acid derivative of a reaction product of sulfur dioxide and an aldehyde-amine product.

2. A process of pickling a metal which comprises subjecting the metal to be pickled to the action of a substantially non-oxidizing acid solution containing a small proportion of a hydrochloric acid derivative of a reaction product of sulfur dioxide and an aliphatic aldehyde-aromatic amine reaction product.

3. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a hydrochloric acid derivative of a. reaction product of sulfur dioxide and an aldehyde-amine product.

4. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a hydrochloric acid derivative of a reaction product of sulfur dioxide and an aliphatic aldehyde-aromatic amine reaction product.

5. A process of pickling products which comprises iron and steel subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a hydrochloric acid derivative of a reaction product. of sulfur dioxide and an aldehyde derivative of a Schiffs base.

6. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a hydrochloric acid derivative of a reaction product of sulfur dioxide and an gliphatic aldehyde derivative of a Schiifs ase.

7. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a hydrochloric acid derivative of a reaction product of sulfur dioxide and a material formed by reacting an aliphatic aldehyde containing less than eight carbon atoms with a primary aromatic amine.

8. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a hydrochloric acid derivative of a reaction product of sulfur dioxide and a material formed by reacting substantially three molecular proportions of acetaldehyde with substantially two molecular proportions. of aniline.

9. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a product formed by reacting substantially one-half a molecular proport'ion of sulfur dioxide with substantially one molecular proportion of the reaction product of substantially three molecular proportions of acetaldehyde and substantially two molecular proportions of aniline and further reacting the product thus formed with substantially one molecular proportion of hydrochloric acid.

10. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a product formed by reacting in the presence of acetone substantially one-half a molecular proportion of sulfur dioxide with substantially one molecular proportion of the reaction product of substantially three molecular proportions of acetaldehyde and substantially two molecular proportions of aniline and further reacting the material thus formed with substantially one molecular proportion of substantially 35 to 39% hydrochloric acid.

11. A pickling bath for metal products which comprises a substantially non-oxidizing mineral acid solution containing a small proportion of a hydrochloric acid derivative of a reaction product of sulfur dioxide and an aldehyde-amine product.

12. A pickling bath for metal products which comprises a substantially non-oxidizing mineral acid solution containing a small proportion of a hydrochloric acid derivative of a reaction product of sulfur dioxide and an aliphatic aldehyde-aromatic amine reaction product.

13. A pickling bath for iron and steel products comprising a sulfuric acid solution containing a small proportion of a hydrochloric acid derivative of a reaction product of sulfur dioxide and an aldehyde-amine product.

14. A pickling bath for iron and steel products comprising a sulfuric acid solution containing a small proportion of a hydrochloric acid derivative of a reaction product of sulfur dioxide and an aliphatic aldehydearomatic amine reaction product.

15. A pickling bath for iron and steel products comprising a sulfuric acid solution containing a small proportion of a hydrochloric acid derivative of a reaction product of sulfur dioxide and an aldehyde derivative of a Schiffs base.

16. A pickling bath for iron and steel products comprising a sulfuric acid solution containin a small proportion of a hydrochloric aci derivative of a reaction product of sulfur dioxide and an aliphatic aldehyde derivative of a Schifts base.

17. A pickling bath for iron and steel products comprising a sulfuric acid solution containin a small proportion of a hydrochloric acid derivative of a reaction product of sulfur dioxide and a material formed by reacting an aliphatic aldehyde containing less than eight carbon atoms with a primary amine.

18. A pickling bath for iron and steel products comprising a sulfuric acid solution containing a small proportion of a hydrochloric acid derivative of a reaction product of sulfur dioxide and a material formed by reacting substantially three molecular proportions of acetaldehyde with substantially two molecular proportions of aniline.

19. A pickling bath for iron and steel products comprising a sulfuric acid solution containing a small proportion of a product formed by reacting substantially one-half a molecular proportion of sulfur dioxide with substantially one molecular proportion of the reaction product of substantially three molecular proportions of acetaldehyde and substantially two molecular proportions of aniline and further reacting the material thus formed with substantially one molecular proportion of hydrochloric acid.

20. A pickling bath for iron and steel products comprising a sulfuric acid solution containing a small proportion of a product formed by reacting in the presence of acetone substantially one-half a molecular proportion of sulfur dioxide with substantially one molecular proportion of the reaction product of substantially three molecular proportions of acetaldehyde and substantially two molecular proportions of aniline and further reacting the material thus formed with substantially one molecular proportion of substantially 35 to 39% hydrochloric acid.

In testimony whereof I hereunto afllx m si ature.

y gn DEAL H. TOMPKINS. 

